2. This is how dopamine behaves in your brain without drugs.

Orange dots are dopamine. They start off in the neuron at the top of the image before it receives a signal (the yellow flash) to release them into the gap between the brain cells. They then travel across the gap and bind to the purple dopamine receptors at the other neuron. Once they’ve begun the process again by triggering a signal in the second neuron, they can go back to their starting point.

4. This is what happens when you take amphetamines.

Amphetamines (dark dots) mimic dopamine. They bind to dopamine receptors (purple) and trigger the same response as dopamine would. But the amphetamines then make it harder for dopamine to re-enter the first neuron, so more dopamine than usual is left in the gap between the brain cells.

This high concentration of dopamine leads to feelings of euphoria. Another neurotransmitter called norepinephrine is thought to cause the feelings of alertness you get with amphetamines.

But eventually dopamine levels in the brain are depleted. When a regular amphetamine user stops taking the drugs it can take weeks for their dopamine levels to return to normal, making you feel terrible.

5. And when you take cocaine.

Cocaine (dark shapes) prevents the re-uptake of dopamine into the first neuron, so more of it stays in the gap. There it ends up stimulating the second neuron more and increasing the reward, making you feel happy and even euphoric.

As well as this, when you drink alcohol at the same time as taking cocaine, your liver makes a molecule called cocaethylene. This binds to the first neuron even better than cocaine alone, making the effect more extreme.